FYI: High CPU Usage Under Some Conditions

[huntharo]

I have been using oha a lot for my projects and wanted to share that the Tokio async runtime causes a lot of CPU usage under certain conditions.

You might want to consider documenting this or adding a command line arg for it.

As an example:

• Testing the warp server: https://github.com/the-benchmarker/web-frameworks/tree/master/rust/warp
• oha and warp reach ~130k RPS out of box
• oha uses ~300% CPU to achieve this on a 12 core M2 Max
• However, if the number of Tokio worker threads is restricted to 2, the same RPS rate is achieved but the CPU usage is reduced to 150-180%
• Example command: TOKIO_WORKER_THREADS=2 oha -c 100 -z 10s http://127.0.0.1:3000/user/12345667

Incidentally, I made a couple of YouTube videos about this and used oha to test both my framework and other frameworks. You can see oha's histogram dancing around for about 10-15 minutes across the two videos. I thought you might like to see that!